Process for producing a mixture of high-purity c{11 aromatic hydrocarbons

ABSTRACT

High purity C8 aromatic hydrocarbons are produced by prefractionating a C6-400* F. naphtha feed fraction into a 270* F. to 275* F. endpoint fraction and catalytically reforming this 270* F. to 275* F. endpoint fraction to produce a reformate having a minimum of C9+ hydrocarbons. The reformate is then passed to a deoctanizing zone and a rerun column zone to recover a mixture of high-purity C8 aromatic hydrocarbons.

O United States Patent 1151 3,635,815 Kuchar 1451 Jan. 18, 1972 PROCESS FOR PRODUCING A [56] cued MIXTURE 0F HIGH-PURITY c UNITED STATES PATENTS I AROMAT C HYDROCARBONS 2,653,175 9/1953 Davis ..260/674 [72] Inventor: Paul J. Kuchar, Des Plaines,1ll. 3,069,351 12/1962 Davis ....208/ 138 3,384,570 5/1968 Kelley et al. ...260/674 X [73) Ass'gnee' 3'1"? Pmdms cmnl'any Des 3,499,945 3/1970 Kirk ...260/674 3,540,996 11/1970 Maziuk et a1. ..208/92 [22] Filed: July 2, 1969 Primary Examiner-Herbert Levine [21 App]. No.: 838,619 AttorneyJames R. Hoatson, Jr. and Joseph R. Marcus 52 0.5. CI ..208/95, 208/92, 208/134, 1571 ABSTRACT 260/674 High purity C aromatic hydrocarbons are produced by [51 ll!!- Cl ..Cl0g 35/00 prefmctionating a 400 F naphtha feed fraction into a 270 [58] Freld of Search ..208/92, 95, 138, 134; 260/674 F to 275 F endpoint fraction and catalytically reforming this 270 F. to 275 F. endpoint fraction to produce a reformate having a minimum of C hydrocarbons. The reformate is then passed to a deoctanizing zone and a rerun column zone to recover a mixture of high-purity C aromatic hydrocarbons,

2 Claims, 1 Drawing Figure H/gn Purity G Aromatic Hydracarbons 3 Crude Tower Reforming Zane Feed Splitter To Heavy Motor Fuel To Motor Fuel Blending Deoctanizer Column Re for/n er PATENIED Jun 8 m2 INVENTOR; Paul J. Kuchar wtz m 2 m EB Q u 5. K 8:

A TTOR/VEYS PROCESS FOR PRODUCING A MIXTURE OF HIGH- PURITY C AROMATIC HYDROCARBONS BACKGROUND OF THE INVENTION This invention relates to a process for producing a mixture of high purity C aromatic hydrocarbons. It particularly relates to a process for producing a mixture of high-purity C aromatic hydrocarbons having an aromatic hydrocarbon purity of greater than 98 liquid volume percent.

It is well known in the prior art that the conventional scheme for synthesizing and purifying C aromatic hydrocarbons from a naphtha utilizes a reforming system and some form of an extraction device for bulk removal of aromatic followed by fractionation facilities to obtain high-purity C aromatic hydrocarbons and particularly the pure xylenes.

l have found that it is possible to produce a mixture of highpurity C aromatic hydrocarbons by processing a naphtha utilizing my flow scheme which includes the steps of prefractionation, catalytic reforming and postfractionation. I have further found that by utilizing a particular prefractionation step and by operating the reforming zone at a severity particular to the fractionated naphtha qualities and by postfractionation of the reformate, a stream of high-purity Cg aromatic hydrocarbons (para-xylenes, meta-xylenes, ortho-xylenes and ethylbenzene) with an aromatic purity of greater than 98 liquid volume percent at a xylene recovery of approximately 90 liquid volume percent, based on refonnate, may be produced.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a process for producing a mixture of high-purity C aromatic hydrocarbons.

It is another object of this invention to provide a process for producing a mixture of high-purity C aromatic hydrocarbons in a more facile and economical manner.

It is a further object of this invention to provide a process for producing a mixture of high-purity C aromatic hydrocarbons having an aromatic hydrocarbon purity of greater than 98 liquid volume percent.

Therefore, the present invention provides a process for producing a mixture of high-purity C aromatic hydrocarbons which comprises the steps of: (a) introducing a C -400 F. naphtha feed fraction into a feed splitter prefractionation zone; (b) splitting said fraction into an overhead fraction having a 270 F. to 275 F. end point and a bottoms fraction having a higher end point; endpoint c) introducing said overhead fraction having a 270 endpoint; to 275 F. endpoint into a catalytic reforming zone maintained under reforming conditions sufficient to produce a reformate having a minimum of C,,+ hydrocarbons; (d) passing said reformate into a deoctanizer zone wherein a C hydrocarbon fraction is separated from a C hydrocarbon fraction; (e) passing said C hydrocarbon fraction into a rerun column zone wherein a mixture of high-purity C aromatic hydrocarbons is separated from a C hydrocarbon fraction; and, (I) subsequently recovering said mixture of high-purity C aromatic hydrocarbons.

As will he described hereafter in greater detail, the essence of my invention comprises tying in end point control of the overhead fraction leaving the feed splitter prefractionation zone and the nonaromatic content of the reformate charge to the severity of the reforming operation as measured by the reformate target octane number or the temperature at which the reforming zone is maintained at a given space velocity. I have found that it is necessary to prefractionate the C -400 F. naphtha feed fraction into an overhead fraction having a 270 F. to 275 F. end point (ASTM) in order to minimize the concentration of the C paraffins and heavier which, when reformed, produce constituents which boil within the xylene boiling range. It is then necessary to operate the reformer, charging the 270 F. to 275 F. endpoint naphtha at such a severity that sufficient hydrocracking of the naphtha C material occurs to minimize their final concentration in the reformate.

My invention can be most clearly described and illustrated with reference to the attached drawing which is a schematic representation of a preferred embodiment of my invention.

DESCRIPTION OF THE DRAWING Referring now to the drawing, a naphtha containing feed is passed via line 1 into crude tower 2 which is a conventional crude tower such as is found in any typical refinery complex. A C 400" F. naphtha feed fraction is removed from crude tower 2 via sidecut means 5 via line 6 and passed into a feed splitter prefractionation zone 7. Hydrocarbons lighter than the C 400" F. naphtha will be removed from crude tower 2 via line 3 and heavier hydrocarbons removed from tower 2 via line 4.

The feed splitter prefractionation zone 7 is operated so that an overhead fraction having a 270 F. to 275 F. endpoint is separated from a bottoms fraction having a higher end point. Typically, the feed splitter will operate at a bottoms temperature of 300 F. to 400 F. and the bottoms fraction is removed from feed splitter 7 via line 8 and passed to a heavy motor fuel reformer (not shown). The overhead fraction having a 270 F. to 275 F. endpoint is passed via line 9 into catalytic reforming zone which is maintained under reforming conditions sufficient to produce a reformate having a minimum of C hydrocarbon. It has been found that when the overhead fraction having a 270 F. to 275 F. endpoint comprises from 2 to 5 liquid volume percent C naphthenes plus parafiins, the reforming conditions shall include a C reformate clear target octane of from 92.0 to 96.0. When the overhead fraction having a 270 F. to 275 F. endpoint comprises greater than l0 liquid volume percent C naphthenes plus paraffins, the reforming conditions shall include a C reformate clear target octane of greater than 100.0.

As will be apparent to one skilled in the art, the reforming zone may contain any suitable reforming catalyst known in the art including those catalysts comprising refractory inorganic oxides such as alumina, which are-combined with at least one metal from Group VIII of the Periodic Table and, if desired, a halogen component as well as those reforming catalysts utilizing a crystalline aluminosilicate as the catalyst support. Reforming conditions include a temperature in the range of from 800 F. to 1,100 F. or more, and preferably a temperature in the range of from 850 F. to 1,050 F., and a pressure in the range of from 50 p.s.i.g. to about 1,000 p.s.i.g. or more, and preferably from 100 p.s.i.g. to 1,000 p.s.i.g. The reforming zone may be maintained at a liquid hourly space velocity of 0.1 to 20.0 or more, and preferably in the range of from about 0.5 to 15.0 or more, and a gaseous liquid hourly space velocity in the range of from 100 to about 3,000 or more. It is further apparent to one skilled in the art that the 270 F. to 275 F. endpoint overhead feed fraction may be passed through the reforming zone in an upward, downward or radial manner.

The reformate passes from reforming zone 10 via line 11 into a deoctanizer zone 12 wherein a C naphthene and lighter hydrocarbon fraction is separated from a C aromatic and heavier hydrocarbon fraction. The deoctanizer may be a conventional fractional distillation column and is usually maintained at a pressure of about p.s.i.g. and a bottoms temperature of from about 300 F. to about 350 F. The top temperature is maintained in the range of from about 200 F. to about 300 F. The C naphthene and lighter hydrocarbon fraction is passed from deoctanizer 12 via line 13 to a motor fuel blending facility (not shown). The C aromatic and heavier hydrocarbon fraction is then passed from deoctanizer 12 via line 14 into a rerun column zone 15 wherein a mixture of highpurity C aromatic hydrocarbons is separated from a C hydrocarbon fraction. In the drawing, the high purity C aromatic hydrocarbons are represented as being removed from the rerun column via line 17. The C hydrocarbon fraction is removed from the rerun column via line 16. C -lhydrocarbon fraction is removed from the rerun column via line 16. C fractions find use as a heavy aromatic solvent and may be utilized for motor fuel blending.

It is also contemplated within the scope of this invention that feed treating means (not shown) be placed in such a manner that, for example, the C -400 F. naphtha feed fraction passing via line 6 into feed splitter prefractionation zone 7 be passed through the treating zone for removal of various impurities that may be present. Further, a feed treating zone may also be located in line 9 between the feed splitter prefractionation zone and the reforming zone for removal of impurities from this fraction prior to the fraction passing into the catalytic reforming zone. Feed compound impurities that may be removed include sulfur compound impurities, nitrogen compound impurities, oxygenated compound impurities, and heavy metal impurities that may be present in a conventional naphtha feed.

PREFERRED EMBODIMENT In a particularly preferred embodiment of my invention, this invention provides a process for producing a mixture of highpurity C aromatic hydrocarbons having a aromatic hydrocarbon purity of greater than 98 liquid volume percent which comprises the steps of: (a) introducing a sidecut fraction from a crude unit distillation column comprising a C -400 F. naphtha into a treating zone containing a means for removing sulfur and nitrogen compound impurities from said fraction; (b) removing from said treating zone a treated C -400 F. naphtha feed fraction and introducing said fraction into a feed splitter prefractionation zone; (0) introducing said overhead fraction having a 270 F. to 275 F. endpoint into a catalytic refonning zone maintained under reforming conditions sufficient to produce a reformate having a minimum of C hydrocarbon; (d) passing said reformate into a deoctanizer zone wherein a C hydrocarbon fraction is separated from a stabilized C aromatic hydrocarbon fraction; (e) passing said stabilized C aromatic hydrocarbon fraction into a rerun column zone wherein a mixture of high-purity C aromatic hydrocarbons having an aromatic hydrocarbon purity of greater than 98 liquid volume percent is separated from a C aromatic hydrocarbon fraction; and, (f) subsequently recovering said mixture of high-purity C 8 aromatic hydrocarbons.

It is apparent that the present invention provides a process for producing a mixture of C aromatic hydrocarbons utilizing a process comprising fractionation and catalytic reforming exclusive of extraction. It was found that it was essential to prefractionate the reformate charge to at most 270 F. to 275 F. .endpoint (ASTM) inasmuch as experimentation showed that reformates with a clear target octane of 94 to 102 which were produced from naphthas with an end point of 275 F. to 280 F., when fractionated to separate a 275 F.297 F. xylene heartcut, yielded C aromatic hydrocarbon purities of less than 94 percent and purities as low as 88 liquid volume C aromatic hydrocarbons.

I claim as my invention:

1. A process for producing a mixture of C aromatic hydrocarbons having an aromatic hydrocarbon purity of greater than 98 liquid volume percent by fractional distillation and catalytic reforming, exclusive of extraction, which comprises the steps of:

a. catalytically refonning a naphtha fraction having an end point of 270 to 275 F. and containing from 2 to 10 volume percent C naphthenes plus parafiins at reforming conditions, sufiicient to minimize concentration of C material in the reformate, including a severity determined as follows:

i. for a naphtha containing from 2 to 5 liquid volume percent C naphthenes plus parafiins, a C reformate clear target octane of from 92.0 to 96.0;

ii. for a naphtha containing from 5 to 10 liquid volume percent C naphthenes plus paraffms, a C reformate clear target octane of from 96.0 to 100.0; b. separating the resultant refonnate by fractional distillation into a C,, fraction and a Cg fraction;

c. separating said C fraction by fractional distillation into a C -lhydrocarbon fraction and a C aromatic hydrocarbon fraction having an aromatic hydrocarbon purity of greater than 98 liquid volume percent; and

d. recovering the last-mentioned fraction as the product of said process.

2. The process according to claim 1 wherein said naphtha fraction having a 270 F. to 275 F. endpoint comprises from 2 to 5 liquid volume percent C naphthenes plus paraffins and wherein said reforming conditions include a severity producing C reformate clear target octane of from 92.0 to 96.0.

3. The process according to claim 1 wherein said naphtha fraction having a 270 F. to 275 F. endpoint comprises from 5 to 10 liquid volume percent Cg+ naphthenes plus paraffins and wherein said reforming conditions include a severity producing C reformate clear target octane of from 96.0 to 100.0.

UNITED ems FATE FCE CERTIFICATE OF patent 3,635,815 Dated May 30 i972 PAUL J KUCHAR Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The title of the invention on the first page reading HIGH-PURITY C AROMA TIC" ShOU ld .r'ead ---HIGH-PURITY C? AROMATIC--. C01 umn 1, hne 2, Y

reading "PURITY C" shouid read ---PURI C Signed and vsealed this 19th day of September 1972.

(SEAL) Attest:

EDWARD M.FLEI'CHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents' F ORM PC3-1050 (10-69) USCOMM'DC GOB'IG'POQ U. 5. GOVERNMENT PRINTING OFFICE "I! 0-3O-3S 

2. The process according to claim 1 wherein said naphtha fraction having a 270* F. to 275* F. endpoint comprises from 2 to 5 liquid volume percent C9+ naphthenes plus paraffins and wherein said reforming conditions include a severity producing C5+ reformate clear target octane of from 92.0 to 96.0.
 3. The process according to claim 1 wherein said naphtha fraction having a 270* F. to 275* F. endpoint comprises from 5 to 10 liquid volume percent C9+ naphthenes plus paraffins and wherein said reforming conditions include a severity producing C5+ reformate clear target octane of from 96.0 to 100.0. 